by James B. “Jim” Kea
Area Extension Forestry Agent – now retired
Thursday, February 9th, 2006
“What’s that smelly ooze coming out of my oak tree?” That is one of the common tree questions asked this time of year.
Slime flux is the name given to the oozing or flowing liquid that is often seen during the heat of the summer on the trunk, large limbs, or basal roots of oak, elm, maple, apple, yellow- poplar, birch, hemlock, and willow. It is usually more common on large, older trees than younger ones.
Slime flux is what you see; however, it is caused by a condition inside the tree called wet wood. Wet wood is caused when bacteria invade a wound or injury caused by anything from construction damage to lawn mowing. This invasion, not the injury, is the good part! The bacterial growth creates pH and micro-element conditions in the wood that are undesirable for the development of wood decay organisms. In other words, wet wood is a defense against decay and not the fungi that might eventually cause a cavity to develop.
As time passes, the fermenting wet wood-causing bacteria produces methane gas which pressurizes the fluid in the wood under the bark that has grown over the injury. When enough pressure is created, the gas causes the wet wood liquid to ooze, flux, or bubble through the bark. Once in the oxygen-rich environment on the surface, this odorless and colorless or tan liquid darkens. It may or may not be colonized by yeast-like fungi. If the yeast-like organisms colonize the ooze, they grow and produce a foul, yeast or alcoholic smell. Then the flies, hornets, wasps, and sap beetles begin visiting and feeding on this brew of foamy, frothy, fluxing, fermenting slime.
Wet wood or slime flux will not in itself kill a tree. The fluxing is an outward sign of some type of previous injury to the tree. Whether the tree lives or dies will depend on the extent of the previous injuries and the amount of stress to which the tree has been subjected. If fluxing continues for a long period of time, the flow of liquid can discolor the bark, kill moss and lichens on the bark, or kill grass at the base of the tree.
Avoiding stressing the tree further and providing care that improves growing conditions are the best things you can do for a tree with slime flux. Depending on how much gas the wet wood is producing and how well the tree closes the wound, the fluxing may or may not be recurring.
If the flow, smell, or insects become objectionable, particularly on a tree near the front door or beside the patio, periodically flush the area with a stream of water or very diluted solution of household bleach and water. This will lessen the smell and discourage the insects from congregating.
Keep in mind, this often smelly flux is actually caused by a condition inside the tree that is protecting the tree from more damaging decay organisms. That’s an unusual mixed blessing, isn’t it?